The present invention relates to the indication in a road vehicle of attainment of a prescribed maximum axle load and to the attainment of a prescribed aggregate axle load.
From my U.K. patent number 2,087,674 issued Jan. 9, 1985, it is known to fit to a road vehicle a position transducer which provides an electrical signal representing deflection of a suspension system of the vehicle and to provide in a cab of the vehicle a control and display unit which receives the output signal from the transducer. Generally, the transducer is associated with a particular axle of the vehicle and the control and display unit is capable of providing an analogue representation of that load and the generation of an alarm signal when the prescribed maximum load is attained. It is also known to present a numerical display of the load to which an axle is subjected.
The position transducer incorporated in the known arrangement comprises a housing which is mounted in a fixed position with respect to a chassis of the vehicle and a shaft which protrudes outside and is rotatable relative to the housing. There is mounted on the shaft inside the housing a disc having windows through which beams of light can pass from light-emitting diodes or other suitable sources to sensing elements, each of which responds to the incidence of light from the corresponding LED to provide an electrical output. These outputs are processed to provide an electrical analogue signal which is fed to the control and indicating unit in the vehicle cab. The shaft of the transducer is connected by a linkage with an axle of the vehicle. When vertical movement of the chassis relative to the axle occurs, the linkage turns the shaft of the transducer and the disc carried thereon. It is necessary to adjust the connection between the linkage and the shaft to ensure that the movement of the chassis relative to the axle which occurs as the maximum axle load is approached is properly represented by the output signal from the transducer and so that the control and indicator unit properly indicates attainment of the prescribed maximum axle load.
Over a period of several weeks or months, during which the vehicle is in use,the behaviour of the suspension system changes somewhat so that the deflection of the suspension system when the maximum prescribed axle load is attained differs from the deflection caused by the same load at the beginning of that period. This results in erroneous indication to the user by the control and indicator unit. Either the maximum axle load is exceeded without the user being aware of this or the user is led to believe that the maximum axle load has been attained when the true load is somewhat less. Repair or replacement of any component of the suspension system also is likely to lead to erroneous indication by the control and indicator unit. To correct such erroneous indication by the known system, it is necessary to adjust the connection between the linkage and the shaft of the transducer. Such adjustment can be effected without great inconvenience in a workshop when the transudcer is first fitted to a vehicle. Subsequent adjustment of the connection between the linkage and the shaft of the transducer is generally inconvenient and is therefore likely to be deferred or not carried out at all.